Alter Primary Key Column size used in Merge Repl table

Hi,

I have a database with a merge replication. Recently I wanted to change the size of the primary key column of a table and I failed all the methods I tried.

Ex:

tableItems

ItemCode varchar(30) (Primary Key)

ItemDescription varchar (100)

...

What I want to do is to change the size of ItemCode column to varchar(50).

Please anybody help me with a solution for this.

Thanks in advanced.

Chama